Various contents data is delivered due to the growth of the Internet. A streaming technique to play back audio or video data while downloading is known. Merits of the streaming technique are that a user can select the desired movie or music for 24 hours without distance and time limitation, there is no need to download, and we can obtain multiple data linked to website. In the streaming technique, various techniques shown in Patent Document 1 are known as a copy-protection technology for the contents data.
Patent Document 1: JP, A, 2007-88704